1. Field of the Invention
The present invention relates to a wet type exhaust gas desulfurization apparatus; the wet type exhaust gas desulfurization apparatus can desulfurize exhaust gas by causing the exhaust gas to come into gas-liquid contact with an absorbent inside an absorption tower, and can agitate the absorbent which has accumulated inside the absorption tower.
2. Description of the Related Art
Exhaust gas generated in large combustion facilities, such as a plant, or the like, includes SOX (sulfur oxide), such as SO2 (sulfur dioxide). Accordingly, it is desired to remove sulfur oxides from (i.e., to desulfurize) exhaust gas. In order to desulfurize exhaust gas, a wet type exhaust gas desulfurization apparatus has been widely used, and this wet type exhaust gas desulfurization apparatus desulfurizes exhaust gas by using an absorbent including an alkaline material, such as alkaline metal (this type of exhaust gas desulfurization apparatus will hereafter be simply referred to as a “desulfurization apparatus”). A desulfurization apparatus employs a lime gypsum method, limestone gypsum, a magnesium hydroxide method, a sodium hydroxide method, an ammonia absorption method, or the like. In particular, the limestone gypsum method is used in very many desulfurization apparatuses. In many cases, when the limestone gypsum method is employed, limestone slurry which is produced by suspending a limestone (CaCO3 (calcium carbonate)) in water, is used as an absorbent. Furthermore, an absorbent having a relatively high viscosity is used in a desulfurization apparatus. For example, when limestone slurry is used as an absorbent, the concentration of limestone slurry is generally set in a range from about 10% to 30% by weight.
Typically, a desulfurization apparatus includes: a spray mechanism which sprays a supply liquid into an absorption tower; an oxidization mechanism which oxidizes the absorbent to cause exhaust gas to come into an efficient gas-liquid contact with the absorbent which has accumulated inside the absorption tower; and a circulation mechanism which circulates the absorbent within the desulfurization apparatus. With the above-described configuration, the exhaust gas is desulfurized by coming into gas-liquid contact with the absorbent that has been sprayed from the spray mechanism within the absorption tower. In addition, the absorbent that has accumulated inside the absorption tower, is oxidized by the oxidization mechanism. Furthermore, the absorbent is circulated within the desulfurization apparatus by the circulation mechanism, and therefore, is repeatedly contacted within the desulfurization apparatus.
However, if the flowability of the absorbent is low, a sorbent suspended in the absorbent may settle (this phenomenon will hereafter be referred to as “slurry precipitation”). The phenomenon of slurry precipitation may easily occur in an absorbent accumulated inside an absorption tower. In order to address this phenomenon, a conventional method agitates an absorbent accumulated inside an absorption tower. Japanese Patent No. 3170158 discloses a method using propellers, and the propellers rotate in an absorbent accumulated inside an absorption tower. The rotatable propellers agitate the absorbent. Furthermore, Japanese Patent No. 3486399 discloses an apparatus including multiple pneumatic nozzles, and the multiple pneumatic nozzles spray air to generate a vortex flow of an absorbent that has accumulated inside an absorption tower in a direction of the circumference of the absorption tower. More specifically, in the conventional apparatus, the multiple pneumatic nozzles are arranged in a slant along the direction of turn of the vortex flow. Furthermore, the pneumatic nozzles are arranged apart from one another in the direction of the circumference of the absorption tower. The vortex flow generated by the pneumatic nozzles agitates the absorbent. Note that in most desulfurization apparatuses, the propellers and the pneumatic nozzles are operated and stopped in interlock with related mechanisms, such as a spray mechanism, an oxidization mechanism, and a circulation mechanism.